Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-02-28
2003-02-11
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S443000
Reexamination Certificate
active
06517484
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an imaging system, more particularly to an ultrasonic imaging system. The invention has preferred application in the field of medical diagnosis and treatment. The invention also relates to an associated method.
An ideal medical imaging device would be compact, inexpensive, non-invasive, high resolution, and easily controlled by a physician in a general hospital, office or field environment. The ideal imaging device would enable a diagnostician or treating physician to in effect perform non-invasive dissection, selectively imaging internal structures, and perform minimally invasive or laparoscopic surgery with a facility and clarity as if overlying tissue had been removed.
While substantial advances have been made in recent decades over the traditional techniques of x-ray photography, existing medical image devices still fall far short of the ideal device on one or more criteria. Nuclear Magnetic Resonance and Computer Aided (X-ray) Tomography (MRI and CAT Scanners) offer high resolution and selective viewing of deeply imbedded structures, but neither technique can be reasonably described as “inexpensive”, nor the associated devices as As “compact”. Indeed, these devices, requiring specialized facilities and specially trained technicians for their operation as well as heavy capital investment, account for a substantial segment of the burgeoning cost of medical testing. Rather than being available for use as a tool by generalists or in a bedside or office environment, MRI and CAT scanning devices require specialists working in a special facility. The physical bulk of these machines and their monopolization of bedside real estate makes use in the operating theater impractical for the foreseeable future as well as posing logistical problems for field use, even for organizations with deep pockets. The expense of these machines limits their routine application to patients of the world's richest nations, leaving much of the world's population under served by late twentieth century medicine.
Ultrasonic imaging, relying neither on intense magnetic fields nor on penetrating ionizing radiation but instead on readily generated acoustic fields, holds greater promise as a vehicle for a portable and less resource-intensive diagnostic tool for the bulk of the world's population. The potential market for practical devices of this type is vast. Long before the resources will exist to put an MRI machine in every garage, a high-resolution ultrasonic imaging device could be placed in every doctor's office in every town, easing the unserved bulk of the world's population into care in accordance with twenty-first century medical standards. To date, ultrasound has not realized this promise. Images are relatively low-resolution, and tomographic; i.e., presenting a single slice of a target at a time. Existing devices are relatively simple in conception, displaying output on a CRT screen as a function of time and direction of return in a single azimuth from out going active pulses, and fall short of the promise of producing easily interpretable images of three dimensional structures in real time. It is desirable to produce acoustic imaging devices capable of greater spatial resolution and higher visual realism. “Visual realism” is a measure of the faithfulness to images perceivable if an observer were able to see directly inside a selectively transparent patient, realizing the fantasy of “x-ray vision”; the goal of visual realism entails high resolution, low distortion, and correct perspective. Operation of an ideal medical imaging device should also be user friendly. “User friendliness” emphasizes minimization of special interpretational and operational skills necessary to understand and manipulate device output. User friendliness encompasses intuitive control responsiveness, -including the ability to easily modify device output to focus on structural features of interest. User friendliness and visual realism may be collectively referred to as “perceptual acuity”, which encompasses the ability not only to perceive but to readily manipulate high resolution images of complex structures, as if the structures were accessible to direct sight and manual manipulation. The objective is to build a medical imaging device of high perceptual acuity that is also compact, and at minimal cost.
To effectively reconstruct a three-dimensional image from a static array of acoustic sensors, the array must extend in two spatial dimension. Generally, the greater the resolution desired, the larger the array of sensors required. Higher resolution demands larger arrays. However, if a sufficiently large array of sensors is disposed in a rigid mounting the sensors will necessarily not conform to a particular human body surface: employing a filly rigid array in direct contact with a human body limits the array to dimensions over which a soft portion of the body is deformable. This dimensional restriction restricts both resolution and imaged tissue volume. Alternatively, to permit utilization of larger rigid arrays, a secondary medium with an acoustic transmissivity similar to that of the human body may be interposed in a volume between the array and a skin surface. The secondary medium becomes, for the purposes of image processing, just another volumetric region in a three-dimensional model. Interposition of a secondary medium between array and patient, however, may adversely affect ease of use of an ultrasound imaging device and in particular use of such a device in minimally invasive surgical procedures, where the volume occupied by the secondary medium must be penetrated by surgical instruments.
Deforming a small portion of a patient or extending the relatively acoustically dense region represented by a human body with a secondary medium effectively brings the patient to the sensors. A solution to some of the difficulties outlined above is to bring the sensors to the patient, i.e., to deform an acoustic array to conform to an outer surface of the patient's body. This approach permits utilization of larger array sizes without use of a secondary acoustic medium. Further difficulties are introduced, however.
To reconstruct an image from data collected via an array of acoustic sensors, it is necessary to know the geometric relation or configuration of the sensors; to reconstruct a precise and undistorted image, it is necessary to know sensor positions with precision. Furthermore, since the sensors are brought into contact with a living body which may further be undergoing a medical procedure it is necessary to measure geometric relations between sensors continuously and in real time, particularly if the imaging device is to be used to monitor an ongoing medical procedure.
It is difficult to simultaneously solve for transducer position and target structure utilizing only data received at sensors or transducers via transmission though a target region. Therefore, in order for signals associated with respective transducers to effectively cooperate in construction of an image or three-dimensional model in a system making use of transducers capable of relative movement, it is advantageous to provide an independent means of determining relative transducer positions.
Beyond transducer movement further sources of variation are present in any complex electromechanical system, and an acoustic medical imaging device is no exception. Transducers or other components may require replacement in the course of service, with original and replacement parts of only nominally identical electrical characteristics. Wiring may be replaced or reconfigured, and characteristic values of electrical components may drift with time. Therefore, in addition to having a method of determining the instantaneous configuration of an array of acoustic transducers, it is desirable to provide a method of detecting and compensating for random variations an drift in device characteristics.
A further question to be addressed in development of precise ultrasonic diagnostic tools is the form o
Stirbl Robert C.
Wilk Peter J.
Coleman Henry D.
Lateef Marvin M.
Patel Maulin
Sapone William J.
Sudol R. Neil
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